This project was initiated to study the properties, distribution and physiological role of protein carboxymethyl transferase and its acceptor proteins. Protein carboxymethylase has been found mainly in the cytosol of the three pituitary lobes (posterior, intermediate and anterior). The acceptor proteins are highly localized in the intravesicular fractions. Treating rats with high salt diets results in an increase of protein carboxymethylase and a marked decrease of acceptor proteins in the posterior pituitary. Protein carboxymethylase and its acceptor protein has been found in red cells, platelets and leukocytes. Thrombin stimulates protein carboxymethylation in platelets. Chemotaxic bacterial peptides cause a rapid, transient increase in protein carboxymethylation in leukocytes. There appears to be a direct correlation between the ability of the bacterial peptides to attract the leukocytes and protein carboxymethylation.